As a cat owner, you may have noticed that your feline friend’s eyes seem to glow or shine in low light conditions. This is caused by a reflective layer in the eyes called the tapetum lucidum. The tapetum lucidum reflects light back through the retina, giving cats better night vision. But you may have also noticed that the color of the eye shine can vary from cat to cat. Why is that? The color of a cat’s eye shine is determined by the type and amount of pigment in the tapetum lucidum. Here’s a closer look at why cat eyes can shine different colors.
The Purpose of the Tapetum Lucidum
The tapetum lucidum is a layer of reflective cells located behind the retina in the eyes of many animals like cats. It works like a mirror, bouncing light that passes through the retina back onto the light-sensing cells. This “double dose” of light allows the retina to make the most of low light conditions, giving cats and other animals excellent night vision and ability to see in dim lighting.
| Animal | Has Tapetum Lucidum? |
|---|---|
| Cats | Yes |
| Dogs | Yes |
| Cattle | Yes |
| Deer | Yes |
| Humans | No |
As shown in the table above, the tapetum lucidum is present in cats, dogs, cattle, deer and many other animals, but not in humans. This anatomical difference explains why many animals have superior night vision compared to people.
What Causes the Eye Shine?
In low light, cats’ eyes appear to glow or shine thanks to the light reflecting off the tapetum lucidum. When light enters the eye, it passes through the retina to the tapetum lucidum at the back of the eye. The tapetum lucidum reflects the light back through the retina, giving the light receptors in the retina a second chance to be stimulated. This is why cats’ eyes seem to shine in the dark – you are seeing the light that is reflecting back out of the eye.
The Role of Melanin in Eye Color
The specific color of a cat’s eye shine is determined by the type and amount of melanin pigment in the tapetum lucidum. Melanin is the same pigment that gives skin, hair and eyes their color. Here are the two types of melanin:
- Eumelanin – A dark brown/black pigment
- Pheomelanin – A light red/yellow pigment
Cats with a higher concentration of eumelanin in their tapetum lucidum will have an eye shine that appears brown, orange or reddish. Cats with more pheomelanin will have a blue, green or yellow eye shine.
Common Cat Eye Shine Colors
Here are some of the most common tapetum lucidum colors seen in cats:
| Eye Shine Color | Cause |
|---|---|
| Green-yellow | Higher pheomelanin concentration |
| Blue-green | Very high pheomelanin concentration |
| Yellow | Moderate pheomelanin concentration |
| Orange | Low to moderate eumelanin concentration |
| Red | High eumelanin concentration |
| Brown | Very high eumelanin concentration |
As you can see, the specific melanin content of the tapetum lucidum determines the color cats eyes shine.
Other Factors Affecting Eye Shine Color
While melanin is the primary determinant of eye shine color in cats, other factors can also impact the hue:
- Coat color – Cat coat color is linked to melanin levels. So cats with darker fur will likely have more eumelanin in their tapetum.
- Age – The tapetum lucidum may darken with age, shifting the eye shine color.
- Health – Diseases affecting pigment production can alter tapetum lucidum color.
- Medications – Some medications like canine heartworm prevention can cause temporary lightening of eye shine.
However, in most cats, the melanin concentration at birth will be the primary determinant of eye shine color throughout life.
Do Cat Breeds Have Characteristic Eye Shines?
Some cat breeds are more likely to have certain eye shine colors based on their typical coat and eye colors:
| Breed | Typical Eye Shine Color |
|---|---|
| Siamese | Blue |
| Tonkinese | Green |
| Burmese | Yellow |
| Russian Blue | Green-yellow |
| Bengal | Green or blue-green |
| Sphynx | Green, yellow or orange |
However, eye shine color can still vary quite a bit within a breed. But some breeds exhibit more variation than others.
Is Eye Shine Color Linked to Eye Color?
There is no direct correlation between cats’ eye color (iris color) and eye shine color. For example, a cat can have brilliant copper-colored eyes yet still exhibit a greenish-blue eye shine.
A cat’s iris color is determined by different factors than the tapetum lucidum color. However, since melanin also plays a role in iris pigmentation, there are some tendencies:
- Cats with blue irises often have blue eye shine
- Cats with green/hazel irises may have green, yellow or orange eye shine
- Cats with yellow/golden irises often have yellow or green eye shine
But light-colored irises do not guarantee a matching light-colored eye shine, or vice versa.
Is Heterochromia Related to Eye Shine?
Cats with heterochromia (two different colored irises) may also have two different tapetum lucidum colors:
- The eye with less melanin in the iris may also have lower melanin in the tapetum
- For example, a cat with one blue eye and one golden eye may have blue and greenish-yellow eye shines
But this is not always the case. Some cats with complete heterochromia exhibit the same tapetum lucidum color in both eyes. Overall, the relationship between iris color and tapetum color is complex in heterochromatic cats.
Changes to Eye Shine Over a Cat’s Life
Kittens are sometimes born with little to no tapetum lucidum pigmentation. Their eye shine may appear pink or purple. As melanin builds up in the tapetum over the first weeks and months of life, the eye shine color will change to its adult hue.
As cats grow older, the tapetum lucidum may darken or otherwise shift in pigmentation. An aging cat’s eye shine might change from yellow to green, or from orange to red over time. Unfortunately, these age-related changes usually indicate a deterioration of the eye’s reflective abilities.
Health Conditions Impacting Eye Shine
Certain feline health conditions can affect the tapetum lucidum, altering eye shine color. These include:
- Feline hepatic lipidosis – Nutritional disease may cause yellowish eye shine to fade to pale gray.
- Feline infectious peritonitis (FIP) – Can cause eye shine to fade.
- Ocular melanosis – Cancer leads to melanin accumulation, making shine darker.
- Taurine deficiency – Causes loss of tapetum lucidum pigment.
Any significant change in your cat’s eye shine color, especially fading or loss of color, warrants a veterinary exam. It could signal an underlying medical issue.
Why Does Eye Shine Color Matter?
While eye shine color itself does not really matter, it can provide clues about a cat’s vision capabilities. Here’s why it can be useful to pay attention to your cat’s eye glow color:
- Pale or faded eye shine often indicates deteriorating reflective ability of the tapetum lucidum.
- A darker or intense eye shine generally means the tapetum is functioning optimally to enable good night vision.
- Loss of eye shine can signal medical conditions affecting the eye.
- Monitoring eye shine color from kittenhood into adulthood helps you notice any changes.
So in summary, a vibrant eye shine of any color indicates your cat’s vision is functioning as it should be. But abnormal changes to eye glow color at any life stage can signify health issues requiring veterinary attention.
Conclusion
Your cat’s dazzling eye shine results from light reflecting off the tapetum lucidum, a specialized retinal layer that enhances night vision. The specific color of the glow stems from the concentration and ratio of two melanin pigments in the tapetum. A variety of factors including coat color, age, and health can also influence the hue. While eye shine color itself does not matter too much, monitoring it for changes provides insight into your cat’s vision and health. As long as your feline friend has brightly glowing eyes of any shade, it suggests an optimal reflective surface supporting excellent night sight.
